1. Field of the Invention
The present invention relates to a fingerprint recognition device and fingerprint reading window construction.
2. Description of the Related Art
Instead of the use of a password to confirm an authorized person""s identity, confirmation of the identity of the authorized person is often made by a fingerprint recognition device used for this purpose. In the case of an optical fingerprint recognition device, the surface irregularities of the fingerprint are converted into variations in optical intensity which are then converted into electrical signals (image signals corresponding to the fingerprint) by an image pick-up element and the electrical signals obtained are compared with the electrical signals for the authorized person, which are stored beforehand, and confirmation of the identity of the authorized person is thereby made. In such an optical fingerprint recognition device, a fingerprint reading window that is contacted by the fingertip is provided, and detection light rays from a light source installed on the inside thereof are directed onto the fingerprint reading window, so that the reflected light from this fingerprint reading window can finally be input to an image pick-up element. An example of disclosure of an optical fingerprint recognition device is to be found in Laid-open Japanese Patent Application Number H. 10-289304; however, in all prior art recognition devices, the fingerprint reading window that is contacted by the finger tip is arranged within the case of the fingerprint recognition device and is fitted in such a way that it cannot easily be removed from outside.
However, the fingerprint reading window easily becomes soiled due to repeated contact with fingertips. In particular, it becomes more liable to become soiled when a coating layer such as a silicone film is formed on the surface in order to emphasize variations of optical intensity produced by surface irregularities of the fingerprint. When the fingerprint reading window becomes soiled, accuracy of reading the fingerprint deteriorates, with an adverse effect on the accuracy of recognition of authorized persons. As a result, although, when the fingerprint reading window has been soiled, consideration might be given to replacing this, conventionally, no provision was made for replacing the window member, so the only alternatives were either to replace the entire fingerprint recognition device or to request the manufacturer of the fingerprint recognition device to replace the window member, in which case the fingerprint recognition device could not be used while replacement was being requested.
On the other hand, the detection light rays that are directed onto the window member for fingerprint reading, due to considerations regarding illumination of the entire fingertip, must be planar emitted light. In order to obtain such planar emitted light, conventionally, a construction was adopted in which a multiplicity of light-emitting elements were arranged in dispersed fashion on a substrate arranged facing the window member.
However, with a construction as conventionally in which a multiplicity of light-emitting elements are arranged in dispersed fashion on a substrate, a multiplicity of expensive light-emitting elements must be employed, making the device as a whole extremely costly, and also resulting in extremely large power consumption. In addition, due to the need to disperse the detection light rays from the light-emitting elements sufficiently, considerable separation must be ensured between the substrate and the window member, resulting in the problem that the fingerprint recognition device becomes quite large.
The present invention was made in view of the above circumstances, a first object thereof being to provide a fingerprint recognition device wherein a soiled fingerprint reading window can easily be replaced.
A second object of the present invention is to provide a fingerprint-reading window construction that is suitable for a fingerprint-reading window replacement.
A third object of the present inventions is to provide a fingerprint recognition device wherein the number of light sources can be reduced and miniaturization thereby achieved.
It should be noted that the objects of the present invention are not restricted to what is explicitly stated above, but implicitly include the provision of features, to be described, which are essentially desirable or are expressed as advantages.
In order to achieve the above first object, according to the present invention essentially the following technique for solution is adopted. Specifically, as described in Claim 1, part of the case that constitutes the outer shell of the fingerprint recognition device is constituted by a window member for fingerprint reading, which is composed of an optically transparent member that is formed as a separate element from this case, and the above-mentioned window member is removably mounted with respect to the case from outside the above-mentioned case. By adopting such a technique for solution, the window member for fingerprint reading can easily be mounted/removed with respect to the case, with the result that replacement of a soiled window member can easily be performed.
By separately providing the cover member (which also provides a frame member of the window member) having an aperture covered by a window member, this cover member is made to constitute part of the case and can be freely mounted/demounted from outside with respect to the case. If this is done, the window member can be removed from the case by first of all removing the cover member from the case. Since the periphery of the window member, i.e. the cover member, also tends to become soiled by contact with the fingertip, the cover member can also be replaced jointly together with the window member.
A holding part for holding the window member may also be formed on the cover member; if this is done, by holding the window member on the cover member beforehand, mounting of the window member with respect to the case can be achieved by mounting the cover member with respect to the case, and removal of the window member from the case can be achieved by removing the cover member from the case.
A supporting face for supporting the window member may be formed within the case; this is desirable in that it enables the window member that is pressed by the fingertip to be securely received.
Freely demountable mounting of the cover member with respect to the case may be achieved by using the engagement/disengagement of an abutment part provided on the case and an engagement part provided on the cover member; if this is done, the cover member i.e. the window member may be mounted and removed with respect to the case extremely easily without employing a separate fixing element, such as a screw, or a tool for manipulating the fixing element. Such engagement/disengagement of the abutment part and engagement part, i.e. mounting/removal of the cover member with respect to the case, may be performed by causing the cover member to execute a prescribed movement with respect to the case; as this prescribed movement, for example rocking or sliding of the cover member may be suitably selected.
The inner peripheral portion of the aperture in the cover member may be formed with a pair of left and right cut-away apertures to allow passage of light rays for detection of a fingertip.
A fingerprint recognition device according to the present invention may be employed in suitable applications such as use for control of access to a room.
In order to achieve the second object, according to the present invention, the following technique for solution may be adopted. Specifically, as described in Claim 7, a fingerprint reading window is constructed to comprise a window member made of an optically transparent member and a cover member formed with an aperture covered by this window member, and an engagement part for mounting this cover member is formed on the cover member. By adopting such a technique for solution, the window member may be provided for replacement together with the cover member, which provides a frame member at the periphery of the window member. Also, by mounting using an engagement part, the task of replacement is facilitated.
In order to achieve the third object, according to the present invention, the following techniques for solution are adopted. Specifically, as described in Claim 12, in a fingerprint recognition device of the optical type constructed such that detection light rays from a light source are directed onto a window member for fingerprint reading, the fingerprint recognition device has a light-guide plate arranged such that its plate surface faces said window member, the detection light rays from said light source is input from one end face of said light-guide plate and said detection light rays is thereby turned into planar emitted light emitted from the entire plate surface of this light-guide plate. By this technique for solution, detection light rays from the light source are sufficiently diffused while passing through the light-guide plate and are emitted in planar fashion from the entire plate surface of the light-guide plate. Thanks to the diffusion of the detection light rays by the light-guide plate, it becomes possible to employ a small number of light sources, which is advantageous as regards costs and also enables power consumption to be reduced. Also, the separation between the light-guide plate and the fingerprint reading window member can be made closer, making it possible to miniaturize the fingerprint recognition device and in particular making it possible to reduce its thickness.
Preferably the light-guide plate is arranged in inclined fashion with respect to the window member for fingerprint reading; if this is done, a margin can be ensured in respect of the detection light ray path whereby the reflected light from the window member is led to the image pick-up element.
The light-guide plate may comprise a main plate and a surface plate arranged on the surface of this main plate (surface facing the window member); in this case, a multiplicity of grooves may be formed extending in a direction approximately parallel with the input direction of the detection rays from the light source, while being spaced from one another in the direction approximately perpendicular to the input direction of these detection light rays; the diffusion action produced by the light-guide plate is thereby increased, and the detection light rays emitted in planar fashion can be rectified to uniform light rays by the surface plate.
In order to achieve the first and third objects together, the following techniques for solution can be adopted according to the present invention. Specifically, as described in Claim 18, in a fingerprint recognition device of the optical type constructed such that detection light rays from a light source are directed onto a window member for fingerprinting comprising an optically transparent member, and that the detection light rays reflected by the window member are input to an image pick-up element, the window member is formed as a separate element from a case constituting the outer shell of the fingerprint recognition device and is attached removably to the case from outside the case, a light-guide plate is provided such that the plate surface faces the window member, and the detection light rays from the light source are input from one end face of the light-guide plate, whereby the detection light rays are turned into planar emitted light emitted from the entire plate surface of the light-guide plate. By adopting this technique for solution, replacement of the window member for fingerprint reading can be facilitated and the planar emitted light can be obtained while decreasing the number of light sources.
On the preposition that the above technique for solution is adopted, it is preferred that the optical system may be configured as follows. Specifically, a first reflecting mirror for reflecting the detection light rays reflected from the window member is arranged in the direction of extension of the above-mentioned light-guide plate, a second reflecting mirror, for reflecting the detection light rays reflected by the first reflecting mirror towards the image pick-up lens, is arranged below the light-guide plate, and a holding body is arranged below the window member so that the holding member holds the light source, light-guide plate, image pick-up element, image pick-up lens, first reflecting mirror and second reflecting mirror.
As a result of such configuration as above, all the components constituting the optical engine for comparing fingerprints can be held by the holding body, so that the positional relationship among the components can be established with a high precision. In this case, in order to enable the positional and sizing relationship between the window member and the holding body to be established with a high precision as well, it is preferred to provide the above-mentioned holding body with a supporting face for supporting the window member so that the window member is immovably clamped between the supporting face and the cover member in a condition where the cover member is attached to the case.
The case may be a special-purpose case exclusively for a fingerprint recognition device, or the case of another type of equipment in which a fingerprint recognition device is incorporated, such as the keyboard case in an information processing device typified by a notebook personal computer may be effectively utilized without modification.